RE: positional predicates in XPath vs XQL

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At 21:10 23-11-2001, Howard Katz wrote:
> > From: owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> > [mailto:owner-xsl-list@xxxxxxxxxxxxxxxxxxxxxx]On Behalf Of Christopher
> > R. Maden
> >
> > At 15:35 23-11-2001, Howard Katz wrote:
> > >To my understanding, the same location path in XPath only
> > returns a single
> > >node, <2>. Is my understanding correct?
> >
> > No.  Whence did you acquire it?
>
>Fallacious raciotination obviously.
>
>I'll bite. What is the correct result in the XPath case??

Nodes 2, 5, and 7.

The predicate filters its context node set, selecting the nodes for which 
the predicate is true.  A numeric predicate n is equivalent to the full 
predicate position() = n.

Your example was the XPath /section/para[1] and the tree

1  section
2       para
3       para
4  section
5       para
6  section
7       para
8       para
9       para

[Note that this is not a well-formed XML document, though XPath can work on 
well-formed text entities such as this.]

The XPath is equivalent to the expanded syntax 
/child::section/child::para[position()=1].  The first / selects the root 
node.  The next expression selects all <section> children of the root - 
nodes 1, 4, and 6 in your example.  The next expression, child::para, 
selects nodes for each node in its context.  For node 1, nodes 2 and 3 are 
selected; for node 4, node 5 is selected; for node 6, nodes 7, 8, and 9 are 
selected.  For each node set, the predicate is evaluated, returning true 
for nodes 2, 5, and 7, as they are each the first in their node set.

~Chris

P.S. YM "ratiocination".  HTH.  HAND.
- -- 
Christopher R. Maden, Principal Consultant, HMM Consulting Int'l, Inc.
DTDs/schemas - conversion - ebooks - publishing - Web - B2B - training
<URL: http://www.hmmci.com/ > <URL: http://crism.maden.org/consulting/ >
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